Carbon fiber reinforcement polymer and its respective application technique for the strengthening of concrete structures

ABSTRACT

The present invention consists of a carbon fiber reinforcement polymer (CFRP) laminate matrix and its application technique on the reinforcement of concrete structures. The present carbon fiber reinforcement polymer (CFRP) laminate matrix comprises a clip or cane shape and it is comprised by two or three rectilinear segments connected by one or two transition areas. This product is meant to be applied on the civil construction area.

TECHNICAL FIELD

The present application describes a carbon fiber laminate and the respective technique to reinforce concrete structures.

PREVIOUS ART

In several cases of projects of reinforcement of armed concrete (AC) structures, the need for reinforcement to flexing demands additional measures to the cut in order to avoid the occurrence of this type of rupture which is frail and that, generally, shows no signs of its occurrence. Thus, for these cases the rehabilitation practice undergoes the application of two reinforcement systems, one for flexing and another for cutting. A similar situation also happens for slabs, where sometimes the need for reinforcement regarding negative momentum forces a reinforcement to puncturing.

The two inventors, Prof. Joaquim Barros from Universidade do Minho, and Eng. Filipe Dourado, CEO of Clever Reinforcement Iberica—Materiais de Construção Lda., have intense collaboration on the investigation on the laminate area regarding carbon fiber reinforcement polymers (CFRP—Carbon Fiber Reinforcement Polymer) applied according to the internationally designated technique for Near Surface Mounted (NSM), and which in Portuguese can be termed as “Instalação próximo da superficie”. Since the beginning of the current century, Eng. Filipe Dourado has collaborated with the ongoing investigation by Prof. Joaquim Barros on the use of CFRP laminates applied with the NSM technique towards the reinforcement of concrete structures, brickwork and wood. The efficiency of this technique regarding the reinforcement of beams and concrete slabs (BA) to flexing has been evaluated [1-3] and also regarding BA beam cutting [4,5], as well as to increase the reinforcement to flexing and energy dispersion from the BA pillars when applied together with CFRP mantle strips involving the section of the element being reinforced, in order to increase the concretes confinement [6]. The binding conditions of the applied CFRP laminates according to the NSM technique have been properly investigated [7]. Recently, the joint use of CFRP systems for reinforcement to flexing and cutting, either from the experimental investigation [8] or numerical [9] standpoint was explored, triggering the opportunity for the laminate concept that it is intended to develop under the present project. The extraordinary efficiency on the reinforcement to cutting of rods which were inserted in beams opening run was recently explored, having been demonstrated that it is possible to convert fragile cutting failure modes into flexing cuts in ductile failure modes [10].

The knowledge heritage acquired by the inventors in the past fifteen years on the subject of structure reinforcement with composite materials has allowed a deep understanding of the advantages and frailties of the current systems. The disadvantages of the reinforcement techniques which resort to Fiber-Reinforced Polymers (FRP) are ultimately its early rupture by detachment, especially when resorting to the externally bonded reinforcement (EBR) and its susceptibility to high temperatures and acts of vandalism. When applied according to the NSM technique, the CFRP laminate reinforcement ability is also not fully mobilized, due to the premature occurrence by detachment of the recoating concrete where the laminates are inserted, or by sliding alongside the substrate.

GENERAL DESCRIPTION

The present request describes a carbon fiber reinforcement polymer (CFRP) matrix laminate and its application technique on the reinforcement of concrete structures. More specifically, the request describes a CFRP laminate with a clip shape, formed by three straight segments and two transition areas, or canes, constituted by two rectilinear segments and a transition area (elbow), in which the extremity branches ensure reinforcement towards cutting in beam like elements or puncturing in slabs, while the rest of the laminate ensures reinforcement towards flexing. This product is meant to be applied in the construction area.

Analytical and numerical analysis studies, as well as parametric studies performed with these models provided privileged information that are the ground for the CFRP laminate now being presented. Indeed, the developed laminate results of a transformation of a laminate currently produced by Clever Reinforcement Iberica—Materiais de Construção Lda in its Elvas factory, where a developed mechanism allows to execute the transition areas (elbows) which grants the laminate with the clip or cane shape configurations.

These configurations assure the reinforcement ability to the laminate to, simultaneously, flexing and cutting of BA beams, flexing and puncturing of BA slabs, and anchor flexing regarding pillars, balconies, panels and related elements. The base of the CFRP laminate has a constant through-cut section, which can range in width from 10 and 20 mm, with a thickness of 1.4 mm.

The extremities of the CFRP laminate are introduced in opened punctures on the section of the element to be reinforced, similarly to the Embedded Trough Section (ETC), which demonstrated an extraordinary efficiency on the reinforcement of armed concrete beams [10]. The laminates inclination and extremity length depend on the reinforcement being executed, whereby they are presented with the reinforcement project. The largest and most complete experimental program performed to date regarding CFRP laminates applied to the reinforcement to cutting according to the NSM technique [4] has demonstrated that the efficiency of this technique regarding the reinforcement of BA beams cutting significantly depends on the inclination of the laminates, the quality of the surrounding concrete, the percentage of stirrups on the beam to be reinforced, and the hardness of the reinforcement systems. On the other hand, the results on the efficiency evaluation tests of the ETS technique on the reinforcement to BA beams cutting has demonstrated that due to the fact that the reinforcement elements are within the section, a far superior level of efficiency is guaranteed when compared with the NSM and EBR techniques. Such is due to the greater confinement offered by concrete which envelops the reinforcement elements when using the ETS technique, as well as a bigger fracture surface which is developed during the removing process of the reinforcement elements which go through the cutting clefts. These conclusions were also confirmed by the presented parametric studies [5].

In order to evaluate the potential of a new type of laminate, standard CFRP laminates were manually transformed, in order to be with the intended configuration, namely clip or cane, and a preliminary experimental exploratory program consisting of armed concrete beams and slabs was made, where it was possible to observe the greater efficiency of these new laminates and its respective reinforcement technique, relatively to laminates and traditional techniques, as it is shown on FIGS. 7 and 8, as the clip or cane configuration with the extremity (extremities) inserted into the section are very efficient on the reinforcement to cutting/puncturing. Such is due to the increased confinement that the surrounding concrete gives to the laminate, a bigger concrete fracture resistant surface during the removing process of a laminate with a potential cutting slot across, and the anchoring effect of the center of the laminate used for the reinforcement to flexing. In turn, the efficiency of the reinforcement to flexing is far superior to the one achieved with standard CFRP laminates applied according to the NSM technique, as the extremities of the new laminate, when introduced in punctures executed inside the section, assure and extraordinary anchoring effect to the middle part of the laminate used in the reinforcement to flexing. Therefore, the laminates critical area is the transition between the three segments that form this new laminate, two regarding the cane configuration (elbows). These areas are made through a mechanism designed to ensure the proper inclination without loss of rigidity and resistance. These areas are thermo-mechanically treated, keeping a plait configuration, and being jacketed with a fiber sleeve.

Thus, the results of the experimental, analytical and numerical investigation, along with the already performed exploratory results, show that the proposed laminate has a superior efficiency when compared to what is assured by the existing nowadays. The extremities of this new type of laminate, being inserted on the section of the part being reinforced, are more protected against the nefarious action of high temperatures, when compared with the current marketed FRP systems. Therefore, even under fire, the new types of laminates work as tendons, in which its anchoring matches with the extremity areas of the laminate that are embedded in the concrete according to the ETC technique. This type of laminate can also be used on the reinforcement to flexing of pillars and cantilevers/consoles, balcony types and related, with full mobilization of the CFRP laminate traction resistance. In this case, the laminate extremities are inserted, with the intended anchorage inclination and length, in openings made on the pillars or cantilevers or consoles connecting elements.

The present FCRP laminate has the ability of, simultaneously, serve as reinforcement to flexing and cutting regarding BA beams, and flexing and puncturing regarding BA slabs. It can also be applied on the reinforcement to pillar, balcony and console flexing, where the folded extremity, regarding the case of a laminate with only one folded extremity—named as a cane type laminate—is inserted in a puncture executed on the concrete element where the laminate will be anchored. The reinforcement ability of this laminate is higher than any other FRP system currently in the market, given that the highest traction extension possible to be mobilized nears the ultimate traction extension of the material, being possible in most cases to achieve the final extension, as observed in the made exploratory experimental assays, as well as in the performed numerical simulations. The reinforcement technique for the application of this new type of laminate also contributed to its biggest reinforcement efficiency, given that beyond the benefits derived from a good laminate anchoring, its extremities are protected from the nefarious action of high temperatures, whereby the laminate, even under fire, develops a reinforcement ability, as if it is a tendon, much larger than any existing FRP system. The use of an epoxy (S&P 55) adhesive which fills the spacing between the laminate and the substrate on the puncture area by means of its own weight, given its high fluidity, allows a more complete and quick filling than the currently existing systems.

Throughout this request it is considered that an elevated fluidity equals a viscosity between 850 e 1150 mPa*s.

The nature of this new type of laminate and the reinforcement technique is based on the accumulation of solid knowledge supported by experimental, numerical and analytical investigation performed during the last 15 years on FRP and structure reinforcement areas.

This investigation allowed to demonstrate that the CFRP laminates of rectangular section, when applied according to the NSM technique, are more effective on reinforcement to flexing than the systems applied according to the EBR technique. This comes from the fact that the laminate is confined within a groove which is on the coating concrete, whereby its separation by detachment, observed on systems applied according to the EBR technique, it is not observed on the laminate applied according to the NSM technique. Beyond this, the analytical and numerical models have shown that the bigger the ratio between the perimeter of the laminate and the area of the through-cut section, the bigger its fixation capacity to the concrete substrate [2]. However, the high tension concentration on the extremities of the CFRP laminates applied according to the NSM technique leads to detachment of the concrete coating, which starts in those areas and progresses throughout almost the entire laminate, given that the maximum mobilized extension can be significantly lower than the last extension on the laminate traction. Thus, by having folded extremities on the laminate, inserted into punctures made on the section of the part to be reinforced, a precocious detachment is avoided, and the critical areas of the laminate are protected against the nefarious action of high temperatures typical of a fire.

On the other hand, the investigation performed on the reinforcement to cutting with CFRP laminates applied according to the NSM and ETS techniques has shown that the reinforcement efficiency is higher when the ETS technique is used, given the higher confinement assured by the surrounding concrete [10]. By such fact, in the proposed laminate, its extremities are applied according to the ETS techniques, but now resorting to the rectangular section laminate due to the already stated fact of this geometry assures better fixation conditions than circular section reinforcement. Besides that, the adhesive to be applied on these areas, with elevated fluidity, will ensure a faster and more complete space filling between the laminate and the surrounding substrate.

Intervals and Possible Variations

The efficiency and profitability of the reinforcement technique depends on the rigor assured for the required length and inclination of the laminate, as well as the quality and rigor on the execution of the transition areas. However, an error below 10% whether on the inclination or the length of the extremities does not affect significantly the performance of the new type of laminate and the respective reinforcement technique, as well as the quickness of execution of such technique. An equal error level is admitted regarding the execution of a puncture for the laminate extremities, as well as its diameter. These relatively high tolerances are justified by the adequate flexibility of the laminates transition area, which allows for some work adjustment regarding the laminates extremity inclination. The extremity inclination of the laminate can range from 30 to 90 degrees with the beam axis (or the slab plane, and it should be the closest from orthogonal regarding the cutting slots (beams) or puncturing (slabs). Considering the cutting and puncturing rupture modes observed on armed concrete beams and slabs, respectively, the laminates extremities inclination should be close to 45 degrees, but a variation of +/−15 degrees is perfectly acceptable (inclinations of 30 to 60 degrees), and the assumption of vertical extremities (orthogonal regarding the beam axis or the slab plane) can still be an effective alternative when difficulties on the execution of inclined puncturing are a considerable obstacle for technical/economic reasons. The length of each of the parts that make up for the laminate, will be completely dependent on the conditions of the reinforcement project, but a 10% error does not compromise its efficacy. However, the higher the length of the laminates embedment on the BA element section to be reinforced, the greater the efficiency of the reinforcement to cutting/puncturing.

BRIEF DESCRIPTION OF FIGURES

To better understand the technique, the figures are present in annex, which represent preferable embodiments which, however, are not intended to limit the object of the present disclosure.

FIG. 1 shows a clip type of CFRP laminate.

FIG. 2 shows a cane type of CFRP laminate.

FIG. 3 shows a clip type laminate application for the reinforcement to flexing and cutting of armed concrete beams.

FIG. 4 shows a clip type laminate application for the simultaneous reinforcement to flexing and puncturing of armed concrete slabs.

FIG. 5 shows a clip type laminate application for the simultaneous reinforcement to flexing of armed concrete pillars with laminate extremity anchoring.

FIG. 6 shows a cane type laminate application for the reinforcement the negative momentum of swinging armed concrete structures, with the example of a balcony.

FIG. 7 shows a beam reinforcement.

FIG. 8 shows an exploratory assay on the use of the new types of laminates for reinforcement to BA slabs flexing and puncturing: a) laminate configuration; b) reference slab rupture by cutting; c) reinforced slab rupture by flexing with a 30% increase on the cargo capacity and 33% on the straining ability, using a small percentage, executed by a manual process of laminate transformation.

DESCRIPTION OF THE EMBODIMENTS

Hereafter, some embodiments will be described in a more detailed manner, which however are not intended to limit the scope of the present disclosure.

The present disclosure describes CFRP laminates as the ones shown on FIGS. 1 and 2, as well as the concrete structures reinforcement technique using these laminates.

Types of Laminates

The laminates shown of FIGS. 1 e 2 are elaborated from transverse section laminates 1.4×10 mm² or 1.4×20 mm². The transformation, executed by an automatism, introduces the transition areas (Tz), elbows, presented on the referred figures, being the laminate able to take a clip shape (FIG. 1) or a cane shape (FIG. 2). The transition area is executed by a thermo-mechanical treatment, in which by temperature rise, with an oven existing in the mechanism, the adhesive becomes viscous, in a way that it becomes possible to assure the required inclination to the laminates extremity. This process is followed by application of a rotational movement to the parte formed by the transition area and its corresponding laminate extremity, while the other part of the laminate is kept fixated, being this way introduced a plait configuration to the transition area. This area is then dipped in an adhesive and jacketed by a fiber sleeve in order to achieve the intended hardness, being the process finalized by curing of this area.

In FIG. 1 it is precisely shown a representation of the CFRP laminate with a clip shape with both of its extremities folded, being able to yield two different inclinations (Θ1 and Θ2). The laminate is formed with three branches: central with a length of Lb, which has the fundamental function of guaranteeing a reinforcement to flexing of the BA element to be reinforced; both extremities, whose behavior can be different, LS1 and LS2, which have as the main objective of reinforcement to cutting. These branches are connected by a transition area (TZ), that arises from a complementary thermo-mechanical treatment with a fiber jacket in order to assure the required resistance and hardness to avoid precocious ruptures as a consequence of a development of tension gradient caused by the variation on the orientation on the parts of the laminate and the existence of different anchoring conditions on the laminates parts.

In FIG. 2 a representation of a cane type CFRP laminate with a folded extremity is shown, being able to take the intended orientation. The laminate is formed by two branches, one with a Lb length for reinforcement to flexing, and another with a Ls length which can serve as a reinforcement to cutting and/or to assure an adequate anchoring from the reinforcement laminate to flexing. These branches are connected by a transition area (TZ).

Reinforcement Techniques

The reinforcement technique consists of installing the laminate part destined to the reinforcement to flexing (Lb on FIGS. 1 e 2) in a slot made on the BA concrete element coating to be reinforced (area with a L1 and L2 length as shown on FIG. 3a ) and on the installation of the extremity (extremities) of the laminate in previously opened punctures on the section of the element to be reinforced (FIGS. 3a, 3e and 3f ). After the execution of the slot and puncture, they are cleaned by compressed air or an equivalent technique. The slot should have a width (ag) between 4.5 and 5.5 mm (FIG. 3g ) and a height (bg) equal to the added laminate from 1.0 to 3.0 (FIG. 3g ). On the other hand, the punctures diameter should be equal to the largest dimension of the added laminate section from 1.0 to 3.0 mm (FIG. 3f ). Before introducing the laminate in the slot and punctures, the laminate is cleaned with a degreasing agent. The adhesive for fixation on the concrete of the Lb part of the laminate, S&P 220, is produced according to the recommendation of the adhesives manufacturer, although another adhesive can be used as long as it is demonstrated by detachment assays that the equal or superior conditions on the fixation of the laminate to concrete are achieved, and applied with spatula, tube or other nozzle mechanism in order to completely fill the slot with the adhesive, throughout the length Lb and part of the transition area in order to seal the lower part of the punctures. On the laminates sides (10 or 20 mm wide), throughout the Lb length, a thin adhesive layer is applied, and the laminate is immediately introduced on the slot and their punctures. After the laminates are applied, and while assuring a curing period for the adhesive of at least 24 hours, a high fluidity adhesive is introduced by gravity, on the top of the punctures, in order to fixate the laminate extremities to the surrounding concrete (FIGS. 3e, 3f and 3h ). The curing period for the two types of used adhesives should be the one stated by the manufacturer of such adhesives.

The clip shaped laminates are especially suited for the simultaneous reinforcement of beams flexing and cutting. In the example shown on FIG. 3a , a beam with a T section and reinforced for positive momentum and transverse effort, resorting to a clip laminate (L1) disposed along the longitudinal symmetry plane of the beam, as shown on FIG. 3c , and by two clip laminate (L2) disposed along the beam, near the beams sides, as shown on FIG. 3b . Throughout the L1 length, the beam is reinforced to flexing with 3 laminates, as shown on FIGS. 3a and 3d , while on the L2 lengths the beam has only 2 laminates for reinforcing to flexing, as shown on FIGS. 3a and 3c . The central part of the laminates (Lb) assures reinforcement to flexing, and offers resistance against the propagation against flexing clefts (Crf), while the laminates extremity parts (Ls) assure reinforcement to cutting (Crs). The side parts of the laminate, while inclined, are inserted into opened punctures on the beams section, with a diameter equal to the bigger side of the laminate section, bf, as shown on FIG. 3e . After the laminate is installed, the puncture is filled with high fluidity adhesive in order to fill by gravity the existing spaces between the laminate and the puncture wall, as shown in FIGS. 3h and 3 f.

The clip laminates, as shown of FIG. 4, are also proposed for the simultaneous reinforcement to flexing and puncturing of BA slabs. The central branches are used towards reinforcement to flexing but also assure anchoring to the extremity branches, while such extremity branches have the main function of reinforcement to puncturing and anchoring to the central branch of reinforcement to flexing. The central branches offer a resistance to flexing cleft propagation (CRf), while the extremity branches offer resistance to cutting clefts opening and sliding (CRs).

The clip or cane laminates, as shown on FIG. 5, can also be used for the reinforcement to flexing of pillars, whereas the non-inclined part has the function of reinforcement to flexing and the extremity (extremities) to assure the needed anchoring in order to an effective reinforcement to flexing, avoiding a precocious detachment.

The cane laminates, as shown on FIG. 6, are indicated particularly for the reinforcement of negative swing momentum, as it is in the case of the balconies shown in the figure. The laminates horizontal part assures the intended reinforcement to flexing, with a La length, assuring the intended laminate anchoring.

FIG. 7 shows the BA beams reinforcement configuration adopted for the current experimental program.

FIG. 8 shows the BA slabs reinforcement configuration adopted for the current experimental program—FIG. 8a , brittle rupture by registered puncturing on the reference slab, as shown on FIG. 8b and ductile rupture by flexing of the reinforced slab with the new types of CFRP laminates, as shown on FIG. 8 c.

REFERENCES

1. Sena-Cruz, J. M.; Barros, J. A. O.; Coelho, M.; Silva, L. F. F. T., “Efficiency of different techniques in flexural strengthening of RC beams under monotonic and fatigue loading”, Construction and Building Materials Journal, 29, 275-182, 2011.

2. Barros, J. A. O.; Dias, S. J. E.; Lima, J. L. T., “Efficacy of CFRP-based techniques for the flexural and shear strengthening of concrete beams”, Cement and Concrete Composites Journal, 29(3), 203-217, March 2007.

3. Barros, J. A. O., Fortes, A. S., “Flexural strengthening of concrete beams with CFRP laminates bonded into slits”, Cement and Concrete Composites Journal, 27(4), 471-480, 2005.

4. Dias, S. J. E.; Barros, J. A. O., “Shear strengthening of RC beams with NSM CFRP laminates: experimental research and analytical formulation”, Composite Structures Journal, 99, 477-490, 2013.

5. Bianco, V., Barros, J. A. O., Monti, G., “Three dimensional mechanical model to simulate the NSM FRP strips shear strength contribution to a RC beam: parametric studies”, Engineering and Structures, 37, 50-62, 2012.

6. Perrone, M., Barros, J. A. O., Aprile, A., “CFRP-based strengthening technique to increase the flexural and energy dissipation capacities of RC columns”, ASCE Composites for Construction Journal, 13(5), 372-383, October 2009.

7. Costa, L G.; Barros, J. A. O., “Critical analysis of fibre-reinforced polymer near-surface mounted double-shear pull-out tests”, Strain—An International Journal for Experimental Mechanics, doi: 10.1111/str.12038, 2013.

8. Costa, L G., Barros, J. A. O., “Flexural and shear strengthening of RC beams with composites materials—the influence of cutting steel stirrups to install CFRP strips”, Cement and Concrete Composites Journal, 32, 544 553, 2010.

9. Barros, J. A. O.; Costa, I. G.; Ventura-Gouveia, A., “CFRP flexural and shear strengthening technique for RC beams: experimental and numerical research”, Advances in Structural Engineering Journal, 14(3), 559-581, 2011.

10. Barros, J. A. O.; Dalfre, G. M., “Assessment of the effectiveness of the embedded through-section technique for the shear strengthening of RC beams”, Strain International Journal, 49(1), 75-93, 2013.

The present technology is not, naturally, in any way restricted to the embodiments described in this document and a person skilled in the art could predict many technology modification possibilities without straying from the general idea, such as defined on the embodiments.

All embodiments above described are obviously interchangeable. The following claims define additional preferred embodiments.

The present technology is not, naturally, in any way restricted to the embodiments described in this document and a person skilled in the art could predict many technology modification possibilities without straying from the general idea, such as defined on the embodiments.

All embodiments above described are obviously interchangeable. The following claims define additional preferred embodiments. 

1. A carbon fiber reinforcement polymer matrix laminate with a clip or cane shape and comprising slots for the insertion of carbon fiber sheets, high fluidity adhesive material, armed concrete structure—beam, pillar, slab and foundation, T section beam, embedment on the interior section, stirrups, coating concrete and two or three rectilinear segments connected by one or two transition areas (Tz).
 2. A carbon fiber reinforcement polymer matrix laminate according to claim 1, presented with a constant through-cut section with a width between 10 and 20 mm and a thickness of 1.4 mm.
 3. A carbon fiber reinforcement polymer matrix laminate according to claim 1, in which the inclination of the extremities can range between 30 to 90 degrees regarding the beam axis or the slab plane.
 4. Laminate reinforcement method for the carbon fiber reinforcement polymer matrix laminates described in claim 1, comprising the following steps: Opening a slot on the element of coating concrete from the armed concrete to be reinforced; Puncture opening with a diameter equal to the maximum dimension of the laminates through-cut section plus between 1.0 and 3.0 mm; cleaning of the slot and punctures with compressed air; cleaning of the laminate with a degreasing agent; adhesive execution and its application throughout the length of the slot, and application of a thin layers of said adhesive on the sides of the laminate; introduction of the laminate part for reinforcement to flexing through the slot, and the parts of the laminates extremity; after curing the adhesive, fill the spaces between the external parts of the laminate and the puncture walls with high fluidity adhesive.
 5. Reinforcement method regarding the carbon fiber reinforcement polymer matrix laminate according to claim 4, in which the coating concrete slot is comprised between 4.5 and 5.5 mm.
 6. (canceled) 